We plan to investigate aspects of the kinetics, morphology and energy needs of protein transport into developing vitellogenic mosquito oocytes. 125I-labeled mosquito yolk protein will be used to determine the kinetics. Questions of optimal conditions, possible turnover of sequestered protein and the specificity and rate of specific uptake will be probed. Both homologous yolk protein and heterologous proteins will be used in these experiments. Electron microscopic visualization of the process will focus on the site of initial binding, receptor localization in coated pits, vesicle formation and its possible dependence on yolk protein, coated vesicle to naked vesicle transitions, fusion with the yolk granule and the site of blockage due to inhibition of glycolysis. Ferritin or horseradish peroxidase covalently bound to the protein serves to render the protein visible in the electron microscope.